1. Field of the Invention
The present invention relates generally to cellular mobile communications systems where a location register is provided to maintain mobile records, and more specifically to an efficient method of locating a mobile station from the mobile switching center when there is a need to access the mobile station.
2. Description of the Related Art
In a cellular mobile communication network, base station areas are assembled into a plurality of location areas and in each location area the base stations are further assembled into a number of control groups. Base stations of each control group are connected to a base station controller. The current mobile locating process of a cellular mobile communication network involves the use of a database called a location register which is usually provided in a mobile switching center to which a number of base station controllers are connected. Mobile stations are constantly receiving base station identification codes and location area identification codes from surrounding base stations. When a mobile station crosses a boundary between adjacent location areas, it sends a location update request containing its mobile identification code and the codes received from a nearby base station.
This request is relayed through the nearby base station and through a corresponding base station controller to the mobile switching center, where the location register is updated according to the request from the mobile station. If there is an incoming call destined for the mobile station, the mobile switching center looks up the location register and identifies its location area and all base station of the location area. The mobile switching center proceeds to broadcast a paging signal to the identified base stations. As a result, copies of the paging signal are broadcast simultaneously from such base stations in search of the called mobile station. If the mobile station is located in one of the base station areas, it sends a response message, which is relayed through the base station and the base station controller to the mobile switching center.
However, since the paging signal is broadcast from all base stations of a location area, even a single page significantly increases the amount of network""s downlink traffic.
It is therefore an object of the present invention to provide a cellular mobile communication network and method of communication for efficiently locating a mobile station.
According to a first aspect of the present invention, there is provided a cellular mobile communication network including a plurality of base stations for respectively covering base station areas, the base station areas being assembled into a plurality of location areas and the base station areas of each location area being assembled into a plurality of control groups. The network comprises a first database for maintaining a plurality of mobile records, each of the mobile records indicating one of the base station areas when a mobile station crosses a boundary between adjacent location areas and enters the base station area. A second database is provided which is associated with one of the control groups of base station areas for maintaining a plurality of mobile records, one of the mobile records indicating a base station area when the mobile station successively crosses a boundary between adjacent base station areas of one of the location areas. A first controller is responsive to a call request for accessing one of the mobile records in the first database to identify one of the control groups of base station areas and producing a search request. A second controller is associated with one of the control groups of base station areas, the second controller being responsive to the search request for accessing one of the mobile records of the second database and transmitting a paging signal to at least one base station area indicated in the accessed mobile record to wait for a response from the mobile station and broadcasting the paging signal to remaining base station areas of the identified control group if the response is not returned from the mobile station.
Preferably, the mobile station is arranged to transmit a message indicating that the mobile station is crossing the boundary between adjacent location areas, and the first controller responds to the message for creating the mobile record in the first database and returning an acknowledgment message to the mobile station. The mobile station is further arranged to transmit a message indicating that the mobile station is crossing the boundary between adjacent base station areas, and the second controller responds to the message for creating the mobile record in the second database and returning no acknowledgment message to the mobile station.
According to a second aspect, the present invention provides a communication method for a cellular mobile communication network including a plurality of base stations for respectively covering base station areas, the base station areas being assembled into a plurality of location areas and the base station areas of each location area being assembled into a plurality of control groups. The method comprises the steps of (a) maintaining a plurality of mobile records in a first database, each of the mobile records indicating one of the base station areas when a mobile station crosses a boundary between adjacent location areas and enters the one base station area, (b) maintaining a plurality of mobile records in a second database associated with one of the control groups of base station areas, one of the mobile records indicating a base station area when the mobile station successively crosses a boundary between adjacent base station areas of one of the location areas, (c) accessing one of the mobile records in the first database in response to a call request and identifying one of the control groups of base station areas and producing a search request, (d) accessing one of the mobile records of the second database in response to the search request, (e) transmitting a paging signal to at least one base station area indicated in the accessed mobile record to wait for a response from the mobile station, and (f) broadcasting the paging signal to remaining base station areas of the identified control group if the response is not returned from the mobile station.